It's a great side-scrolling shooter at heart, but is crippled by one majour flaw.
While the graphics have aged, they do their job. The textures are decent, and the animation is fast and smooth as it should be. The combat is fast, and it can be great fun at times, but there's a severe flaw: It's way too easy. It makes sense that Duke's health bar is his Ego since hes known for being so egotistical. It even makes sense that when he downs an enemy, his Ego gets bigger. But unfortunately, that novelty wears thin very, very quick. The combat has almost no challenge, as each enemy you down gives you more Ego expanding your life. Power ups are plentiful, and so are enemies, making power ups almost useless. I got bored and switched from easy to medium, and you still got health from beating foes. I switched to hard, and you STILL get health from beating foes. The only difference is its a bit less than in other skill levels. (3 health instead of 10 in easy or 5 in medium) and the bigger the baddie, the more ego you get. As I said, the context works, but it wears thin quickly. It's a shame too, because the level design is excellent. The only real challenge here comes from some tricky platform based puzzles, some that cleverly take a 'pseudo-3D' feel as they go in a cylindrical shape. Boss fights are also a tad anti-climactic. Remember the boss fights from Duke Nukem 3D? Their silliness yet awesomeness made them great. Anybody remember the final boss? Putting him on a football and having his grunts in football uniforms made the boss fight instantly 10x more memorable than it would've been otherwise, simply because of the silly but playful humour. The bosses in Manhattan Project are often underwhelming, and they could've easily been better if they at least added some humour to them. They are perfectly forgettable, and that's a shame as well considering the standard enemies all have the DN flavour of silliness and fun.
This game is a good game overall, but it's somewhat disappointing. It has all the substance to be a great game, but certain design choices simply bring it down. It's still a fun game, and it has a healthy dose of the Duke Nukem charm. Its goofy, its funny, its stupid, its violent, but its fun. That's what makes Duke's games great. The level design is also spectacular, but combat falls flat in several areas. If you like Duke Nukem, you'll be doing yourself a favour by playing this game. It shouldn't be very expensive, and it's a treat for anyone that loves Duke. Even if you don't like Duke, but like old school 2D shooters, than you should still pick this game up, once again, its a treat to see a game like this in the modern era. Just don't expect it to rock your world like DN3D did.